This invention relates to data acquisition and, in particular, to analog to digital conversion of an electrical signal.
As known in the art, transducers are used in a host of applications to convert the effect of some phenomenon into an electrical signal. The pervasiveness of the digital computer requires that the signal be in digital form for storage, analysis, or other manipulation. Since many transducers produce analog signals, these must be converted to digital form. In this conversion, some information is inevitably lost.
For example, if a transducer produces an output signal which varies smoothly from zero to five volts, converting the signal to digital form introduces discontinuities or steps in the signal in which information is lost. It is therefore desirable to obtain as small a step as possible. A problem with this goal is the fact that size of the step is directly related to the number of bits used to quantify the information. If a converter had a resolution of eight bits, then the five volt range could be divided into two hundred fifty-six discrete steps, each step spanning approximately twenty millivolts. If the converter had a resolution of twelve bits, the five volt range could be divided into four thousand ninety-six steps of about one millivolt each.
The greater resolution appears highly desirable until one starts to consider the time it takes to manipulate the data or the storage requirements for the data. One is then faced with the problem of trying to resolve apparently contradictory requirements of high speed and high resolution.
It should be noted that, as used herein, "resolution" and "accuracy" are distinct concepts. One may divide an interval into any number of steps but this says nothing of how well the conversation relates to the input signal. The former relates to resolution, the latter to accuracy. In implementing the present invention, currently available hardware is sufficiently accurate.
In view of the foregoing, it is therefore an object of the present invention to increase the apparent resolution of an analog to digital (A/D) converter.
Another object of the present invention is to provide a means for monitoring selected portions of a process.
A further object of the present invention is to provide high speed, high resolution A/D conversion.
Another object of the present invention is to provide a means capable of adapting itself to the observed data.
A further object of the present invention is to provide adaptive window means for acquiring or monitoring data.
Another object of the present invention is to provide an A/D converter having vernier resolution.